1. Field of the Invention
The present invention relates generally to devices for assisting a traveling control apparatus used in electric vehicles. More particularly, the present invention relates to devices for achieving an improvement in overall traveling performance.
2. Description of the Related Art
Recently, attention has been focused on electric vehicles, such as automobiles, powered by electric motors for traveling as next-generation vehicles as substitutes for conventional gasoline vehicles using internal combustion engines. It is expected that electric vehicles powered by clean electric energy can basically solve environmental problems such as detrimental exhaust gas and noise of automobiles. The exhaust gas is said to be responsible for about 70% of air pollution. Moreover, one of the other benefits of electric vehicles is that the life of petroleum resources can be prolonged by at least twice as much.
The electric vehicle typically has road wheels suspended from a vehicle body through shock absorbers. This construction is similar to a conventional automobile. The electric vehicle includes an electric power system comprising a battery power supply made up by a plurality of storage cells, an electric motor for providing rotational energy, a motor driving circuit for controlling rotation of the motor, and a control circuit for instructing control commands to the motor driving circuit. The driving forces generated by the motor is transmitted through a power transmitting apparatus to rotatively drive a road wheel for powering a vehicle in a similar manner as conventional.
The battery power supply for supplying electric power to the electric motor is made up by a plurality of storage cells connected in series so as to provide a required voltage. The storage cells each have a characteristic as follows. With the elapse of time during which the storage cell is discharged in use, the terminal voltage of the battery cell is gradually lowered as shown in a discharge curve in FIG. 11, and then reaches the final voltage at the curve end. When reaching the final voltage, no current must be flown from the storage cell for protection of the storage cell. It is also known that, as shown in FIG. 12, the discharge curve depends on currents supplied in use and changes in the supplied current vary the time during which the storage cell can be discharged continuously. Therefore, an electric vehicle includes a capacity meter for accurately displaying, based on any of various methods, the amount of electric energy remaining in the storage cell while the electric vehicle is in operation.
The electric power from the power supply is supplied through the motor driving circuit which performs chopper control to increase or decrease an effective voltage supplied to the motor for controlling a rotational speed of the motor. A chopper duty ratio for control of the effective voltage is commanded from the control circuit which is electrically connected to an accelerator grip or the like of a manipulation device. In other words, depending on the opening degree of the accelerator set by a driver operating the manipulation device, the control circuit sets a duty ratio for the chopper control and outputs it to the motor driving circuit. Thus, in accordance with an increase or decrease in the opening degree of the accelerator set by the driver, the control circuit sets a duty ratio for the chopper control and, based on this duty ratio, the motor driving circuit increases or decreases the effective voltage supplied to the motor, thereby providing the rotational speed of the motor corresponding to the opening degree of the accelerator.
Further, in place of an engine brake conventionally effected by an internal combustion engine, an electric vehicle generally employs a regeneration brake which is effected by using the electric motor for traveling as a dynamo. The regeneration brake serves as an auxiliary brake such that kinetic energy to be reduced when the electric vehicle decelerates or travels down over a slope, is converted into electric energy by temporarily using the electric motor as a dynamo. Then, it is also customary to charge storage cells with the regenerated electric power for recovery of energy.
Moreover, an electric vehicle is generally loaded with various protective devices for protecting equipment. Specifically, the protective device comprises a sensor provided on each relevant equipment for measuring a temperature, a voltage and so on, and determination means for comparing a sensor value with an evaluation reference level, i.e., an alarm/stop level, and determining the operating condition of the equipment. When the first alarm level is detected, this is determined that the equipment has come close to the limit for use, and an alarm is indicated on a display panel or the like to inform the driver of the determination. When the second stop level is detected, this is judged that the equipment has reached the limit for use, and the operation of the equipment is then stopped.
With motor control practiced in conventional electric automobiles, however, because the chopper duty ratio is set in proportion to the opening degree of the accelerator, there has been a drawback that an accelerating ability of the electric vehicle is different depending on the charge conditions of the storage cells and an acceleration feeling in traveling is unsteady. This is attributable to that although the terminal voltage is lowered with consumption of storage cells, the duty ratio is always set depending on the opening degree of the accelerator regardless of how the storage cells are consumed and, therefore, the effective voltage supplied to the motor is lowered, resulting in differences in the accelerating ability and so on.
Also, with the regeneration brake used in conventional electric automobiles, because the amount of chargeable electric power is varied depending on how storage cells are consumed, there has been a problem that the regenerated electric power can not often recovered to the storage cells, regenerative braking forces are reduced, and safety during traveling of electric automobiles can be impaired. To solve the problem, it has been proposed to introduce any surplus electric power, that cannot be recovered to the storage cells, to a large-sized resistor disposed outside the automobile compartment for generating heat from the resistor so that the generated heat is dissipated to open air for consumption of the surplus electric power. Another alternative is to rotatively drive a flywheel by an electric motor using the regenerated electric power for storing the surplus electric power in the flywheel as mechanical energy. But none of these methods is preferred since the total weight of the vehicle is increased, extra mounting space is required, and the structure is complicated.
Additionally, with the conventional protective device, because the operation of the equipment can still be continued after an alarm has been issued from the protective device, there has been a fear that the driver may continue operating the equipment and the equipment may abruptly be stopped in unwanted situations. This means that when the protective device monitors a temperature condition of the motor, by way of example, the vehicle may stall in a place where it should not be stopped, such as an intersection or a railroad crossing. Further, for a protective device arranged such that the motor operation ability is lowered in the alarm stage, there accompanies a serious risk because the traveling speed is reduced and it takes a time to move away from the improper place.
Moreover, because an alarm issued from the protective device is conventionally indicated on a display panel to inform the driver of the situation, there has been a fear that the driver cannot visually confirm the alarm and cannot recognize it depending on traffic situations in the surroundings and/or running conditions. In electric motorcycles such as scooters, particularly, that tendency is increased from the relationship between the position of the display panel and the range of view of the driver.